The proposed project will conduct a controlled evaluation of the impact of changes in the food and physical activity (PA) environments on childhood obesity and related behaviors in five New Jersey cities. These cities have been targeted for interventions by three major initiatives, affording the opportunity to conduct a natural experiment. The study aims are to advance our understanding of the relationship between elements of the environment and childhood obesity and related behaviors, assess the impact of specific environmental interventions, and demonstrate an innovative methodology for controlled evaluation of community interventions. Three research questions and implicit hypotheses will be tested: 1) What is the relative impact of children's exposure to changes in the community food environment, the school food environment, the community PA environment, and the school PA environment on changes in eating and PA behaviors? 2) What is the relative impact of children's exposure to changes in the community food environment, the school food environment, the community PA environment, and the school PA environment on changes in children's weight status? 3) What roles do perceptions of the environment and barriers to access play in these relationships? The research design relies upon a prospective, longitudinal study of a randomly selected panel of 1200 children in these cities. The research team collected comprehensive baseline data on obesity-related behaviors and body mass index in 2009-2010. The data also include documentation of the food and physical activity environments to which these children were exposed (geo-coded for analysis). Comprehensive data collection on children will be repeated in four years and relevant changes in the environment will be monitored over the same period. Changes may include presence of new opportunities for healthy eating or physical activity (e.g., new supermarkets, playgrounds); significant enhancement of existing ones (e.g., addition of healthy foods to convenience stores, expanded physical education in schools), as well as non-intervention related change (e.g., retail outlets that close). Individual-level exposure will be measured by proximity of the environmental change to each child's residence (using geo-spatial methods). The analysis will evaluate the impact of exposure to these changes on a comprehensive set of outcomes including behaviors relevant to food consumption and PA as well as weight status. The research design facilitates an exceptional degree of control in isolating the effects of particular intervention strategies. The project's impact on policy will be amplified by the researchers' extensive relationships with stakeholders in the studied cities, ongoing efforts to disseminate findings from the recently conducted cross-sectional study, and the Rutgers Center for State Health Policy's history of informing state-level policy in NJ and around the nation.